Electrophotographic development apparatus

ABSTRACT

A developing apparatus for an electrostatic reproduction machine includes a nonmagnetic cylinder rotatably mounted relative to a fixed magnetic field generating means. A multicomponent magnetic developer material is fed to the cylinder forming magnetic bristles of developer material thereon for brushing contact with a photosensitive electrostatic plate bearing an electrostatic latent image thereon. A portion of the developer material transfers to the plate developing the image, and the remainder is slung from the rotating cylinder onto a guide member thereby providing marked agitation and recombination of the developer material resulting in an increased triboelectric charge level of the developer material. The magnetic field is oriented to facilitate the slinging of the developer material against the guide. It further provides a directional field following the delivery point of the developer material to the cylinder which prevents developer material from flowing over the outer edges of the magnetic field existing at the development zone and post development zone. The developer material is thus prevented from being attracted to the cylinder at the development zone and thereafter prematurely slung from the rotating cylinder thereby keeping unwanted developer material from being carried away from the developer unit by the plate.

United States Patent [191 Caudill [451 Aug. 28, 1973 1 ELECTROPHOTOGRAPHIC DEVELOPMENT APPARATUS [75] inventor: Allison Holland Caudill, Lexington,

[22] Filed: Dec. 17, 1971 [21] Appl. No.: 209,039

[52] US. Cl. 118/637, ll7/l7.5, 355/3 [51] Int. Cl. G033 l/300 [58] Field of Search 118/623, 636, 637, ll8/D1G. 24, 10 Z; 355/3, 30 D; ll7/l7.5

[56] References Cited UNITED STATES PATENTS 3,626,898 12/1971 Gawron 118/637 3,667,428 6/1972 Smith 118/637 3,648,656 3/1972 Ogawa 118/637 3,641,980 2/1972 Bickmore 118/637 3,638,614 2/1972 Young et al. 118/637 3,640,248 2/ 1972 Nielander 118/637 3,580,673 5/1971 Yang 355/15 3,457,900 7/1969 Drexler 118/637 3,152,924 10/1964 Wanielista et al. 118/637 Primary Examiner-Mervin Stein' Assistant Examiner-Leo Millstein Attorney-John W. Girvin, Jr. et a1.

[57] ABSTRACT A developing apparatus for an electrostatic reproduction machine includes a nonmagnetic cylinder rotatably mounted relative to a fixed magnetic field generating means. A multicomponent magnetic developer material is fed to the cylinder forming magnetic bristles of developer material thereon for brushing contact with a photosensitive electrostatic plate bearing an electrostatic latent image thereon. A portion of the developer material transfers to the plate developing the image, and the remainder is slung from the rotating cylinder onto a guide member thereby providing marked agitation and recombination of the developer material resulting in an increased triboelectric charge level of the developer material. The magnetic field is oriented to facilitate the slinging of the developer material against the guide. It further provides a directional field following the delivery point of the developer material to the cylinder which prevents developer material from flowing over the outer edges of the magnetic field existing at the development zone and post development zone. The developer material is thus prevented from being attracted to the cylinder at the development zone and thereafter prematurely slung from the rotating cylinder thereby keeping unwanted developer material from being carried away from the developer unit by the plate.

5 Claims, 4 Drawing Figures ELECTROPHOTOGRAPH IC DEVELOPMENT APPARATUS CROSS-REFERENCE TO RELATED APPLICATION BRIEF BACKGROUND OF INVENTION 1. Field This invention relates to the developing of latent electrostatic images on a plate and, more particularly, to an improved magnetic brush development apparatus.

2. Description of the Prior Art ln well-known electrostatic printing processes, a sur- .face bearing a latent electrostatic image is developed by applying a developer material comprising toner and a carrier material to the surface. The small toner particles are held onto the surfaces of the relatively large carrier particles by electrostatic forces, which develop from the contact between the toner and carrier particles-producing triboelectric charging of the toner and carrier to opposite polarities. A portion of the applied triboelectrically charged toner is selectively attracted to the image areas of the surface, and the remainder of the developer material is removed and allowed to recirculate to form subsequent images. In order to assure clear, sharp images, it is necessary that the toner obtaina high triboelectric charge prior to-development. This has generally been effected in prior devices by selecting toner and carrier materials which are widely separated in the triboelectric series and by causing agitation and stirring of the developer material prior to development. Further, the ratio of toner to carrier in thedeveloper mix is closely controlled. However, even when the most optimum materials and mixing devices are, utilized, the triboelectric charge of the toner for a given tonercarrier ratio is often insufficient to provide uniform high quality copy output.

Various prior art developing mechanisms incorporate a magnetic brush comprising a cylindrical member rotatably mounted relative to a fixed magnetic field generating means onto which multicompo'nent mag- .netic developer material is delivered. The magnetic field generating means creates a magnetic field causing the magnetic developer to form in bristle-like arrays over the surface of the cylindrical member as it is rotated into contact with an electrostatic latent imagebearing plate. The magnetic field generating means may be housed inside of the cylinder and generates a field which is dimensionally smaller in the axial direction.of the cylindrical memberthan the length of the cylindrical member. Such dimensioning prevents devel- I oper material from accumulating at the edge of the cylindrical member where it can be readily lost from the surface of the cylindrical member and cause machine malfunctions. An example of such magnet placement is described in prior US. Pat. No. 2,786,441.

Since the magnetic field generating means of the prior devices generates a weak field at the edge por- High speed rotation of the magnetic brush unit results in the slinging ofi of the developer material located within the fringe field onto the electrostatic plate and into the general ambience of the developer unit. Since there must be a clearance between the plate carrying the electrostaticlatent image and the developer unit in order that the developed image thereon be undisturbed as it leaves the developer unit, developer material which is prematurely slung off from the magnetic brush often is carried out of the developer unit with the electrostatic plate. In order to prevent such premature slinging off of developer material, prior devices operated at relatively low speeds resulting in developed images which lacked the requisite degree of clarity.

SUMMARY In order to overcome the above-noted shortcomings of the prior art to provide a magnetic brush developer unit which consistently produces clear, sharp, wellfilled images without causing unwanted developer material to be carried into the machineambience, a cylindrical member is mounted for high-speed rotation relative to a fixedmagnetic field generating means which generates mangetic fields which (1) controls the placement of developer material on the cylindrical member, (2) controls the development of the image with the developer material, and (3) controls the high-speed discharge of the developer material from the rotating cylindrical member against a guide member thereby creating a high level of triboelectric charging of the developer material. A magnetic field is generated at the point of delivery of the developer material to the cylindrical member which directs the developer material toward the center of the magnetic brush and away from the edges thereof. A second magnetic field is generated within the development zone which is wider than the first magnetic field along the axial dimension of the cylinder but shorter than the axial dimension of the cylinder, which attracts and holds all of the magnetic material directed thereovenA third magnetic field is created which keeps the magnetic materials strongly attracted to the cylinder until it reaches an optimum release point. The magneticfield is shunted at the release point so that the developer material travels at a high velocity from the cylinder and impactsa guide member positioned to receive the developer material. The im pact effects some separation and a high degree of agitation of the toner and carrier components of the developer material resulting in a high degree of triboelectric charging. The material is returned from the guide member to a sump portion of the developer unit where it is recirculated for subsequent reproduction runs. Since all of the developer material is strongly attracted to the surface, of the cylindrical member until-the cylindrical tions thereof, some developer material is weakly atmember reaches its release point,. virtually no unwanted developer material is carried out with the electrostatic plate as it leaves the developer unit.

Accordingly, it is theprinciple object of the invention to develop clear, sharp electrostatic images in an electrostatic processing system. t

A further object of the invention is to prevent ma- A the invention as illustrated in the accompanying drawings.

in the drawings:

FIG. 1 is a schematic illustration of a conventional electrostatic reproduction apparatus incorporating the electrostatic development apparatus of the present invention.

FIG. 2 is an enlarged cross-section view of a portion of the electrostatic development apparatus of the present invention.

HO. 3 is a schematic pictorial illustration of the magnetic field generating means of the electrostatic development apparatus of the present invention.

FIG. 4 is a.cross-sectional view of a portion of the electrostatic development apparatus of the present invention.

DESCRIPTION Referring now to the drawings, and more particularly, to FIG. 1 thereof, a schematic illustration of a conventional electrostatic reproduction apparatus incorporation the electrostatic development apparatus of the present invention is depicted.

The reproduction apparatus comprises a plurality of processing stations located about a cylindrically shaped electrostatic photosensitive plate 11. The cylindrical plate comprises a layer of photoconductive material superimposed over a conductive nonmagnetic backing. A suitable photoconductive material is disclosed in U.S. Pat. No. 3,484,237 issued Dec. I6, 1969. The photoconductive material is sensitized by a corona generating device 13 as the plate rotates therepast in the direction of arrow 15. A light image of the copy 17 to be reproduced is projected onto the sensitized surface of the electrostatic photosensitive plate 11 rotating thereunderto form an electrostatic latent image thereon. The rotating plate thereafter passes a magnetic brush developing station 19 where multicomponent development material including electrostatically charged toner is applied to the surface of the electrostatic photosensitive plate 11 containing the electrostatic image thereon. The charged toner particles are preferentially attracted to the latent image on the plate 11 and are subsequently transferred to a support surface 21 as the plate rotates therepast by conventional electrostatic transfer or by heat transfer. The plate continues to rotate past a cleaning station 25 which removes residual toner from the surface of the plate.

The magnetic brush developer station 19 which incorporates the electrostatic development apparatus of the present invention contains multicomponent developer material 33 therein. The principle components of the developer material are electroscopic toner and a ferromagnetic carrier material. Suitable materials for use as tonersas well known in the art and generally comprise finely divided resinous materials capable of being attracted and held by electrical charges. Examples of materials which can be utilized for toners are listed in the aforereferenced copending application of William J. Kukla, et al. Many well'known suitable ferromagnetic carrier materials can be utilized, the carrier particles generally being between 50 and 1,000 microns in size. Often, the carrier particles are manufactured by coating a ferromagnetic core or bead with a material which triboelectrically interacts with the se lected toner to produce a desired charge on the toner in order to provide good imaging quality. An example of such a carrier and the method by which it can be made to obtain a desired triboelectric characteristic for any selected toner is disclosed in the aforereferenced copending application of William J. Kukla, et al.

A toner dispensing unit 35 is provided to dispense toner 37 into the multicomponent developer material 33 located in the sump portion 38 of the magnetic brush developing station 19, thereby replenishing toner which is consumed by development of the electrostatic latent image. The counterrotating augers 39 and 40 stir the freshly added toner with the developer material to assure complete mixing thereof as well as to enhance the triboelectric charging of the developer material.

A bucket conveyor 41 rotates through the sump portion 38 of the developing station 19 and scoops up quantities of developer material 33 for delivery to the magnetic brush unit 43. The magnetic brush unit 43 comprises a nonmagnetic, conductive, rotatable cylindrical member 45 having located therein a magnetic field producing means 47. The magnetic field producing means 47 generates a magnetic field which causes the ferromagnetic carrier material to be magnetically attracted to the surface of the cylindrical member 45 and held thereon as the carrier material is delivered from the bucket conveyor 41 and the guide member 48. The cylindrical member 45 rotates in the directions of the arrow 49 under a doctor blade 51 which governs the amount of developer material located on the surface of the cylindrical member 45 as it rotates to a position adjacent the electrostatic photosensitive plate 11. As will be described, the magnetic field producing means 47 creates a normal magnetic field at approximately the 9 o'clock position of the cylindrical member 45 causing the magnetic carrier particles in the developer material 33 to form in bristle-like arrays emanating from the surface of the cylindrical member 45.

The small toner particles of the developer material 33 are held onto the surfaces of the'relatively large carrier particles by electrostatic forces, which develop from the contact between the toner and the outer surface of the carrier particles which produces triboelectric charging of the toner and carrier material to opposite polarities. In the system depicted, the toner particles are triboelectrically charged positively with respect to the negative triboelectric charge on the carrier particles. The total triboelectric charge on the carrier material particles is equal and opposite to the total triboelectric charge on the toner particles. The charge level of this triboelectric charge is dependent upon the selection of materials utilized as toner and carrier (e.g., their relative position on the triboelectric series with respect to one another), the ratio of toner to carrier, and the amount of stirring and agitation impartedto the developer material prior to its delivery to the surface of the cylindrical member 45.

A potential source 53 is connected to the cylindrical member 45 thereby biasing the cylindrical member to a fixed potential. As the magnetically fonned bristles of carrier material containing toner triboelectrically attracted thereto rotate past and in contact with the electrostatic photosensitive plate I], the triboelectrically charged toner particles are attracted to the electrostatic latent image on the plate 11 and adhere thereto. The potential on the cylindrical member 45 correctly orients the electrical field in which the charge toner particles move to thereby produce a uniformly developed image on the surface of the plate 11.

The plate 11 containing the toner particles electrostatically attracted thereto continues to rotate and leaves the magnetic brush developing station 19 at exit point 55. A sealing member (not shown), such as a thin plastic strip, is attached to the outer housing member 57 of the magnetic brush developing station 19 at the exit point 55 in order to prevent large carrier particles which may be adhering to the surface of the plate 11 from rotating with the plate past the magnetic brush developing station 19 and thus being carried out into,

the ambience of the remainder of the electrostatic reproduction apparatus. It should be noted, however, that the sealing member does not contact the surface of the plate 11 in order to prevent the developed image thereon from being disturbed. Thus, dimensionally small carrier particles which may be travelling with the plate I 1 pass through the clearance between the sealing member and the plate 11 at the exit point 55 and are carried out into the reproduction apparatus. As will be described hereinafter, the magnetic field producing means 47 generates a field which prevents such unwanted carryout of small carrier particles.

The developer material which is not transferred to theelectrostatic photoconductive plate 11 is retained on the surface of the cylindrical member 45 as it rotates away from the plate 11 by a magnetic field generated by the magnetic field producing means 47 until it reaches approximately the 6 0clock position of the cylindrical member. The magnetic field producing means 47 is shunted so that the magnetic field rapidly diminishes at the 6 oclock position. Since there is no longer a force holding the ferromagnetic carrier particles to the surface of the rapidly rotating cylindrical member 45 at the 6 oclock position, the developer material located thereon is discharged therefrom. This developer material has an initial velocity which approximates the surface velocity of the cylindrical member 45 at the 6 oclock position. Since the cylindrical member is rotating at a high rate of speed, the developer material is discharged therefrom at a high rate of speed and follows a trajectory path impacting the guide member 59. The

impact force is sufficient to jar loosea quantity of the toner particles triboelectrically attracted to the carrier particles and to cause agitation of the toner and carrier particles of the developer material. The thus separated toner particles recombine with carrier particles as the developer material falls from the guide member 59 into the sump portion 38 of the magnetic brush developing station 19 and during their residency in the sump portion. The recombination of the toner and carrier particlesand the marked agitation thereof at impact produce a high level of triboelectric charging to the developer material resulting in clear, sharp developed images.

A diverter 61 directs that portion of the developer material which drops with a low initial velocity from the surface of the cylindrical member 45 into the sump portion 38 of the magnetic brush developing station l9. The outer housingmember 57 is sloped at a steep angle to prevent developer material from building up adjacent to the exit point 55.

Referring now to FIG. 2 of the drawings, an enlarged cross-section view of a portion of the electrostatic de-' velopment apparatus of the present invention is depicted. As described with respect to FIG. 1 of the drawings, developer material is delivered along the guide member 48 to the surface of the rotating cylindrical member 45. The magnetic field producing means 47 generates a magnetic field which attracts the ferromagnetic carrier material to the surface of the cylindrical member 45.

. I The magnetic field producing means 47 comprises a bar 67 onto which is mounted three magnets, 69, 7], and 73, each of which produces a magnetic field. The bar 67 is made of soft iron or low carbon steel to provide a low reluctance between the magnets. Accordingly, the magnetic fields 75, 77 and 79 as graphically depicted by the dotted lines are produced by the magnets. As can be seen from the graphic illustration, the magnetic field in the area immediately preceding and following the point of adjacency to the doctor blade 51 is approximately tangential to the surface of the cylindrical member 45. The magnetic field at the development zone 8] is approximately normal to the surface of the cylindrical member 45 and the magnetic field following the development zone 81 is again tangential to the surface of the cylindrical member.

The tangential field adjacent the doctor blade 51 effects tight packing of the developer material against the cylindrical member 45 as it rotates under the doctor blade 51, thereby closely regulating the amount of developer material supplied to the development zone. The normal field adjacent the development zone 81 causes the ferromagnetic carrier particles to stand out in bristle-like arrays providing a brush-like surface for brushing contact with the electrostatic photoconductive plate 11. The tangential field following the development zone 81 effects rapid removal of the nonexpended developer material from a position of close adjacency to the rotating electrostatic photoconductive plate 11. The magnetic field 79 produced by the magnet 73 continues to hold the ferromagnetic'carrier particles to the surface of the cylindrical member 45 as it rotates therepast. Once the cylindrical member 45 rotates past the magnetic field 79, there is no longer an attractive force to the ferromagnetic carrier material,

73. The magnet 69 thus tends .to direct developer matev I rial away from the fringe magnetic fields located at the end of the-magnets 71 and 73. Referring now to FIG. 3 of the drawings, a schematic pictorial illustration of the magnetic field generating means of the electrostatic development apparatus of the present invention is depicted. Themagnetic field generating means comprises a bar 67 onto which magnets 69a, 69b,7l and '73 are mounted. The magnets 69a and-69b are depicted as two separate magnets, it being understood that a single-magnet 69 can be utilized in lieu thereof as depicted in FIG. 4 of thedrawings.'The magnets 69a and 69b are set in from the edge of the bar 67 at each end thereof, while the magnets and 73 are approximately. the same length as the bar 67. The bar 67 is shorter'than the axial dimension of the cylindrical member 45, the difference in length being equally distributed at either edge ofthe cylindrical member45. I

As has been described, the magnets 69, 71 and 73 produce magnetic fields 75 and 77 which effect the proper placement of the developer material for optimum image development and which further cause the developer material to be retained on the surface of the cylindrical member 45 until it reaches an optimum release point. Additionally, the magnets 69a and 69b have a fringe magnetic field 83a and 83b, respectively, located about the edge thereof. This magnetic field intersects the nonmagnetic cylindrical member 45 and effects movement of ferromagnetic material located on the cylindrical member within the field along the axial dimension of the cylindrical member 45 toward the center thereof. The developer material located on the surface of the cylindrical member 45 is thus directed away from an area approximate the edge portions of the magnets 71 and 73 and their associated fringe magnetic fields 85 and 87, respectively, as the cylindrical member 45 rotates therepast. By thus directing the developer material away from the fringe magnetic field 85 and into the magnetic fields 75 and 77, developer material is prevented from being prematurely thrown off the surface of the cylindrical member 45. That is, if developer material were allowed to flow over the edge portion of the magnet 71 and within the fringe magnetic field 85, it would be held by the fringe field to the surface of the cylindrical member 45 at the development zone. However, as the cylindrical member 45 rotates past the development zone to the zone 89, the fringe magnetic fields 85 and 87 would not be sufficiently strong in this area to attract the ferromagnetic carrier to the cylindrical member 45. Thus, the carrier particles would be thrown from the cylindrical member 45 at the point 89. With reference to FIG. 1 of the drawings, it can be readily observed that carrier material prematurely thrown from the cylindrical member 45 immediately following the development zone 81 could travel with the rotating electrostatic photoconductive plate 11 past the exit point 55 and be thus carried out into the ambience of the reproduction machine.

Referring now to FIG. 4 of the drawings, a crosssectional view of a portion of the electrostatic development apparatus of the present invention is depicted. As

described with repect to FIGS. 1-3 of the drawings, the

electrostatic development apparatus comprises a cylindrical member 45 which rotates about a stationary magnetic field producing means 47. Rotary motion is imparted to the cylindrical member 45 by the driven pulley 93 which is pinned to the shaft 94 which is connected to the end plug 95 of the cylindrical member 45. The cylindrical member, which may, for example, be 2 5: inches in diameter, is driven at a high speed (in the order of 300 rpm when utilized in conjunction with an electrostatic photoconductive plate travelling at 9.25 inches per second). The magnetic field producing means 47 is mounted to the shaft 96 which is journaled in the end plug 95 at one end thereof and pinned to the support member 97 at its opposite end.

The developer material is delivered to the surface of the cylindrical member 45 between the end plates and 103. The bulk of the developer material is restrained by the end plates I01 and 103 which direct the developer material away from the edge portion of the cylindrical member and away from an area adjacent the edge portion of the magnet 71. However, since there must be clearance 105 and 107 between the end plates 101 and 103, respectively, and the rapidly rotating cylocated between the magnets 71 and 73 wherein a weak a lindrical member 45, some developer material tends to stray underneath the end plates 101 and 103. This developer material would rotate with the rotating cylindrical member 45 past the end portions of the magnet 71 and would be prematurely thrown from the cylindrical member 45 prior to being retained by the magnetic field adjacent the end portion of the magnet 73, unless the material were redirected away from the edge portions of the magnet 71 prior to entering the magnetic field created by the magnet 71. Accordingly, the magnet 69 is positioned to direct developer material which may stray into the clearnce 105 and 107 on the surface of cylindrical member 45 toward the center of the cylindrical member 45 and thus away from the edge portions thereof. The thusly diverted material passes away from the edge portions of the magnet 71 as the cylindrical member 45 rotates therepast.

OPERATION Referring once again to FIG. 1 of the drawings, developer material 33 is delivered by the bucket conveyor 41 and guide member 48"to the rapidly rotatingnonmagnetic cylindrical member 45. The cylindrical member 45 rotates about a magnetic field producing means 47in the direction of the arrow 49 thereby causing the developer mate'rial33, which comprises a ferromagnetic carrier material and toner, to be attracted to and held onto the surface of the cylindrical member 45. The magnet 69 creates a magnetic field which directs the developer material inward along the axial dimension of the cylindrical member 45 away from the edge portions of the magnet 71. The developer material is thus not located on the surface of the cylindrical member 45 adjacent the edge portion of the magnet 71, thereby preventing the developer material from being prematurely thrown off the surface of the cylindrical member 45 after it passes the development zone 81. The magnet 71 creates a normal field at the development zone 81 effecting the formation of bristle-like arrays of developer material on the surface of the cylindrical member 45 thereby providing for optimum development of the latent electrostatic image located on i the surface of the electrostatic photoconductive plate 1 1. The magnet 73 creates a magnetic field which causes the developer material to be retained on the surface of the cylindrical member 45 until the cylindrical member rotates to its 6 0clock position, at which point the developer material is thrown from the cylindrical member onto the guide member 59. The impact of the developer material against the guide member 59 enhances the triboelectric charge of the developer material.

With reference to FIG. 3 of the drawings, the fringe magnetic field 83 created by the magnet 69 directs developer material on the cylindrical member 45 inward along the axial direction of the cylindrical member into the strong magnetic field as the cylindrical member rotates therepast. By thus directing the developer mate rial inward, the developer material does not rotate past the fring magnetic field 85 of the magnet 71. Accordingly, developer material does not reach the zone 89 attractive magnetic field exists. Entry of developer material into this zone would cause it to drop from the surface of the cylindrical member 45, thereby causing a large percentage of this material to be carried out into the ambience of the reproduction apparatus.

While the above description has related to a magnetic brush developer unit wherein developer material is delivered to the upper portion thereof, it is recognized by those skilled in the art that the developer material could be delivered directly from the sump to the undersurface of the rotating magnetic brush. It is only necessary that the magnetic field producing means direct the developer material inward away from the edge of the rotating magnetic brush prior to the time that the developer material reaches the development zone. It is further recognized by those skilled in the art that various magnet configurations can be utilized to effect the generation of the magnetic fields described.

For example, the magnetic field'at the development zone could be created by a magnet located behind the electrostatic plate, and the magnetic field which directs the developer inward along the axial dimension of the cylindrical applicator member could be locatedexternal to the cylindrical applicator member.

Additionally, while a cylindrical applicator member has been described, it is recognized by those skilled in the art that various other forms and shapes of applicator members could be utilized. For example, a belt member which moves relative to the electrostatic plate and developer supply could be utilized without departing from the spirit and scope of the invention.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it should be understood by those skilled in the art that the foregoing and other changes in form and detail may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

l. A developer apparatus for applying multicomponent developer material including magnetically attractable carrier and electrostatically charged toner to an electrostatic plate having a latent electrostatic image thereon for developing said image with toner comprismg: I

delivery means for delivering said developer material to a delivery station;

a movable applicator member having a developer material receiving surface;

7 drive means for moving said surface of the applicator member along a path in a first direction past said delivery station through a development zone adjacent said electrostatic plate and past said development zone, said surface receiving developer material as it moves past said delivery station;

first magnetic field generating means for generating a first magnetic field oriented to intersect a portion of the surface of the applicator member located at the development zone substantially normal thereto for forming developer material located on said portion of the surface into a brush-like array for brushing contact with the electrostatic plate, said first magnetic field extending across said portion of said surface in a direction perpendicular to said first direction from a first field edge to a second field edge;

second magnetic field generating means for generating a second magnetic field oriented to intersect a further portion of the surface of the applicator member located beyond the development zone for retaining carrier and toner adhering thereto on said surface as it moves past said development zone, said second magnetic field extending across said further portion of the surface in a direction perpendicular to said first direction from a first field edge to a second field edge;

third magnetic field generating means for generating a third magnetic field orientated to intersect a part of said surface of the applicator member located between said delivery station and said development zone for moving developer material on said part of said surface toward the center portion thereof from portions of said part of the surface which travel along said path to locations adjacent to said field edges and for retaining developer material located on said part of said surface thereon whereby developer material does not move through the edge portions of the first andthe second magnetic fields as said part of said surface moves through the development zone and past the development zone.

2. The developer apparatus set forth in claim ,1

wherein'said drive means moves said surface past a discharge zone following said development zone, said drive means further moving said surface in a closed loop past said delivery station, said development zone and said discharge zone and wherein said surface moves away from the influence of said magnetic fields at said discharge zone whereby developer material lo' cated on said surface being discharged therefrom as said surface moves past said discharge zone.

3. The developer apparatus set forth in claim 2 further comprising:

a guide member positioned to receive developer material discharged from said surface.

4. The developer apparatus set forth in claim 1 wherein said surface is cylindrically shaped and wherein said drive means imparts rotary movenent of said cylindrically shaped surface about its axis.

5. The developer apparatus set forth in claim 4 wherein said first, said second and said third magnetic field generating means being located within said cylindrically shaped surface. 

1. A developer apparatus for applying multicomponent developer material including magnetically attractable carrier and electrostatically charged toner to an electrostatic plate having a latent electrostatic image thereon for developing said image with toner comprising: delivery means for delivering said developer material to a delivery station; a movable applicator member having a developer material receiving surface; drive means for moving said surface of the applicator member along a path in a first direction past said delivery station through a development zone adjacent said electrostatic plate and past said development zone, said surface receiving developer material as it moves past said delivery station; first magnetic field generating means for generating a first magnetic field oriented to intersect a portion of the surface of the applicator member located at the development zone substantially normal thereto for forming developer material located on said portion of the surface into a brush-like array for brushing contact with the electrostatic plate, said first magnetic field extending across said portion of said surface in a direction perpendicular to said first direction from a first field edge to a second field edge; second magnetic field generating means for generating a second magnetic field oriented to intersect a further portion of the surface of the applicator member located beyond the development zone for retaining carrier and toner adhering thereto on said surface as it moves past said development zone, said second magnetic field extending across said further portion of the surface in a direction perpendicular to said first direction from a first field edge to a second field edge; third magnetic field generating means for generating a third magnetic field orientated to intersect a part of said surface of the applicator member located between said delivery station and said development zone for moving developer material on said part of said surface toward the center portion thereof from portions of said part of the surface which travel along said path to locations adjacent to said field edges and for retaining developer material located on said part of said surface thereon whereby developer material does not move through the edge portions of the first and the second magnetic fields as said part of said surface moves through the development zone and past the development zone.
 2. The developer apparatus set forth in claim 1 wherein said drive means moves said surface past a discharge zone following said development zone, said drive means further moving said surface in a closed loop past said delivery station, said development zone and said discharge zone and wherein said surface moves away from the influence of said magnetic fields at said discharge zone whereby developer material located on said surface being discharged therefrom as said surface moves past said discharge zone.
 3. The developer apparatus set forth in claim 2 further comprising: a guide member positioned to receive developer material discharged from said surface.
 4. The developer apparatus set forth in claim 1 wherein said surface is cylindrically shaped and wherein said drive means imparts rotary movenent of said cylindrically shaped surface about its axis.
 5. The developer apparatus set forth in claim 4 wherein said first, said second and said third magnetic field generating means being located within said cylindrically shaped surface. 